Tall fescue has good forage quality for grazing animals in that it has adequate crude protein and satisfactory digestabilty. However, animals often perform poorly on it and suffer from various disorders such as "fescue foot", characterized in rough coats, weight loss, fever, tenderness or loss of hooves and tails and sometimes death; "bovine fat necrosis", characterized in hard masses of fat along the intestinal tract resulting in digestive upsets and difficult births; and "fescue toxicity", also called "summer slump" because of its common incidence in hot weather, characterized in poor weight gain, reduced conception weights and intolerance to heat.
Higher levels of incidence to fescue toxicosis have been observed in fields infected with certain fungi, in particular endophytic fungi (See Schmidt et al. Journal of Animal Science 55 1260-1263 (1982) Hoveland et al. Agronomy Journal 72 pg 375-377 (1980) and Hoveland et al. Circular 270 from Alabama Agricultural Experiment Station, Auburn University, Alabama (1984)). Certain researchers have compared pastures of tall fescue with and without contamination by the fungus Acremoniun coenophialum and observed a decrease in performance and weight gains and an increase in typical symptoms of fescue toxicosis in pasture with higher levels of A coenophialum contamination (See Hoveland et al. Agronomy Journal 75 pg 821-824 (1983) and Pedersen et al. New Zealand Journal of Experimental Agriculture 14 pg 307-312 (1986)).
The endophyte infection of tall fescue is very wide spread and the fungus is found in the fescue seeds. Thus, the fungal infection is carried over from one season to the next and has been found very difficult to eradicate. Current methods of endophyte control to prevent fescue toxicosis require fields to be chemically treated to destroy the fescue and then planted with other crop for 1,2 or more seasons to allow any residual seeds and their fungal contamination to be killed. Then the field must be planted with seeds specially grown to be free of endophyte contamination. Such procedures are obviously very labor intensive and costly and often will exceeds the savings resulting from the elimination of fescue toxicosis from pasture fed animals. Any savings that might result may then be defeated if the field is later reinfected with the fungus. Obviously the economical treatment of fescue toxicosis has long been a goal of breeders and growers of pasture fed livestock.
Ivermectin is a semi-synthetic member of the class of compounds known as avermectins which are macrocyclic esters which have been discovered to be highly potent antiparasitic agents for animals of both endo and ectoparasites. The compounds have further been found to be highly active as an agricultural pesticide and nematocides against insects which parasitize the aereal parts and roots of growing plants as well as stored agricultural products. Avermectin compounds however are not fungicidal and no reports of any fungicidal activity have been found.